Illuminating Disease: An Introduction to Green Fluorescent Proteins
Marc Zimmer researches green fluorescent proteins as professor of chemistry at Connecticut College, and clearly enjoys his work. Illuminating Disease: An Introduction to Green Fluorescent Proteins is ostensibly a book about the use of such novel chemical markers to signify distinctions—anatomical, functional—in the service of medicine. Yet perhaps its richest contribution is to demonstrate the blurriness of the boundaries, the seemingly inextricably twisted nature of the connections, between so many categories we take for granted as we try to understand and control the world around and within us.
The book begins with the crystal jellyfish, floating in the northern Pacific, emitting green light as their predecessors may have done for nearly 160 million years. A comparatively short time ago, in the 1950s, Osamu Shimomura began his painstaking attempt to understand the underlying mechanism of bioluminescence. Amidst years spent collecting more than a million crystal jellyfish, Shimomura determined the calcium-dependent nature of its bioluminescence; in short, one protein, aequorin, gave off a blue light, which was absorbed by another protein which in turn gave off the energy as green light, hence earning the name “green fluorescent protein,” or GFP. By the early 1990s, following the recombinant DNA technology revolution, Martin Chalfie’s group at Columbia would successfully clone the GFP-encoding gene itself, showing how it could be inserted into model organisms and placed so as to light up in response to particular stimuli (their modified, fluorescing C. elegans worm, with GFP expressed in its touch receptor neurons, famously graced the cover of Science in February of 1994). Soon, Roger Tsien’s own group at the University of California, San Diego improved and expanded the palette, as it were, of GFPs, developing a brighter, more diverse array of fluorescing proteins for scientists to use in their experiments. The GFP revolution itself was off and running. By 2003, over half of the papers in Cell, and 60 percent of the papers in the Journal of Cell Biology, mentioned fluorescent proteins, and in 2008, Osumu Shimomura, Martin Chalfie, and Roger Tsien garnered the Nobel Prize in Chemistry for their efforts. As Zimmer relates, when he first heard about GFP from Doug Prasher (who narrowly missed out on the Nobel Prize itself, as Zimmer sympathetically and touchingly relates) in 1994, there were fewer than 20 people worldwide studying fluorescent proteins; today, they are used in more than 3 million experiments annually to address questions across the wide expanse of biology and medicine.
Zimmer spends the majority of his gorgeously illustrated book tracing the application of such fluorescent protein technology across an ever-expanding array of diseases. In heart disease and cancer, they can be used to tag particular cells and precisely locate them amidst their untagged counterparts, and to monitor their migration throughout model animals (whether mouse fetal stem cells that cross the placenta to come to the aid of the mother’s injured heart, or implanted tumor cells metastasizing and hiding out in less fortunate mice). In infectious diseases like malaria, Chagas disease, dengue fever, influenza, and HIV, where investigators have attempted to disrupt patterns of disease transmission through introducing genetically modified vectors or through vaccines, fluorescing proteins can be used to indicate in which organisms a particular genetic manipulation or immunological response has taken. Transgenically sterilized mosquitoes, indicated by their glowing gonads, are only the most memorable (and not even the most colorful) of such examples. Perhaps the most aesthetically striking use of such technology (as featured on the book’s cover) has been in the anatomical and functional untangling of brain function and dysfunction. The monochromatic drawings of 19th-century neurobiology pioneer (and future Nobelist) Santiago Ramón y Cajal have given way to a rainbow of proteins demonstrating the location and functioning of individual neurons. And in the book’s final chapter, Zimmer turns to the use of light-responsive protein as not just markers, but rather as interventions and potential therapies themselves, through the emerging field of optogentics, in which individual neurons can be turned on and off through focused stimuli.
In heart disease and cancer, green fluorescent proteins can be used to tag particular cells and precisely locate them amidst their untagged counterparts, and to monitor their migration throughout model animals. In infectious diseases fluorescing proteins can be used to indicate in which organisms a particular genetic manipulation or immunological response has taken.
Several themes run implicitly throughout the book. The first relates to Zimmer’s concluding claim that he likes “to think of research projects as puzzles,” and he indeed seems to revel in the Rube Goldberg-like manner of many of the experiments described here, in which multiple biological processes must be linked (proteins switched on, neural connections made, etc.) in order to achieve the rewarding—and revealing—biofluorescent light at the end of a particular experimental tunnel. There is a technical bravura to many of these experiments, even if they often have to be tethered to—and sometimes brought down to earth by—public health or ethical practicalities, such as whether to release genetically modified mosquitoes into a real-world setting. We may admire experiments for their elegance, their utility, or both; but we should keep clearly in mind our reasons for our admiration.
Second, the book serves as an extended reminder of how novel modes of visualization change our worldview, our neat categorizations of structure and function, and especially health and disease. Nineteenth-century scientists exulted over the new worlds opened up by increasingly powerful microscopes and stains, followed at the end of the century by the miracles of the x-ray and fluoroscopy. The 20th century saw successive waves of radiological innovation—ultrasound, computed tomography, magnetic resonance imaging, to name a few—while laboratory scientists could increasingly differentiate and measure cells and even molecules through techniques ranging from electron microscopes and x-ray crystallography to electrophoretic gels, radioimmunoassays, flow cytometry (itself dependent on fluorescence), monoclonal antibodies, and computer programs organizing and displaying enormous amounts of data. GFPs thus join (often, literally) a long line of ever-evolving visualization techniques that continue to modify how we view ourselves, both in the pages of academic journals and in the vernacular.
The book begins with the statement that “scientific breakthroughs can come from the most unexpected places,” and the unforeseen connections between basic and applied science light up throughout the book. So do the linkages between science and commerce, and science and politics, often dictating who will have the funding to develop or apply a novel methodology.
Third, in joining this (very incomplete) list of technologies that came before it, the GFP story points to the life history of such technologies themselves, as they proceed from innovation to the steps taken for granted in the development of further questions, experiments, and innovations. As Zimmer concludes: “Although it is impossible to page through an issue of Science or Nature without seeing an image showing glowing fluorescent proteins, … [i]n real life, fluorescent proteins have become just another tool in the lab that are routinely used and are mentioned only in the methods section of research papers.” It is difficult to tell where this future will lead. Historical inquiry is hard enough, as we apply our own tracers to construct particular depictions, enabled (we hope) through perspective, but always susceptible to the limits imposed by our own methodologies. The future remains still blurrier.
Ultimately, while GFP’s may be utilized to signify differences or distinction, the book in fact reminds us of just how blurry many of our present categories and boundaries remain. Some of these are well-worn themes. The book begins with the statement that “scientific breakthroughs can come from the most unexpected places,” and the unforeseen connections between basic and applied science light up throughout the book. So do the linkages between science and commerce, and science and politics, often dictating who will have the funding to develop or apply a novel methodology. And for the young and enthusiastic at heart (like Zimmer himself, it would seem), it is wonderful to see a blurring between work and play. Zimmer’s description of his children’s designs of Lego castles for their fluorescing pet mice (Shine Shimmer Zimmer and Glowy Glimmer Zimmer ) not only reflects the enthusiasm exhibited throughout the book, but further points to the pleasure some grown-ups get to have in designing their own experiments with slightly more sophisticated (and expensive) tools.
The most obvious blurred boundary in the book, however, is that between art and science. Nearly 200 years ago, John Keats (himself a former medical student) famously wrote, “ ‘Beauty is truth, truth beauty,—that is all Ye know on earth, and all ye need to know,’ ” and artists, scientists, and philosophers have spent parts of the past two centuries exploring the relationship between aesthetics and science. Beyond pragmatics, and even an appreciation for the complexity of experimentation involved in the lab, there is an ineffable beauty to the colorful, novel ways that GFP protein have helped to illustrate and redefine our world. One of the developers of the book’s rainbow cover image of neurons is quoted as saying (prophetically) that GFP techniques are “really good for getting pictures on the covers of journals and books” ). One can certainly sympathize with such transfixed journal and book editors, even if our own sense of wonder remains a mystery to us (for now).